"A massive rainstorm in July 2010 turned city streets into rushing rivers and infamously created a sinkhole so big at N. Oakland and E. North avenues that it swallowed a Cadillac Escalade.

But the flood brought more than rain. It also carried an immense dose of pollutants that washed into waterways.

Big storm events are growing more common. On the Milwaukee River alone, four of the 10 biggest recorded floods have occurred since 1997, according to the Southeastern Wisconsin Regional Planning Commission.

But even with gentle rains, urban and rural runoff is the biggest source of water pollution remaining today."